A scramjet engine is an eminently simple air-breathing jet engine, since it contains no moving parts. That is, a scramjet engine consists basically of a converging inlet, a combustor and a diverging outlet or nozzle. During flight, air flows into the inlet and is compressed. In the combustor, hydrogen or hydrocarbon fuel is injected into the compressed, high temperature airstream and ignited. The resulting combustion expands and increases the pressure of the gases in the combustor, which are then accelerated out of the nozzle to a higher velocity than the inlet air. The reaction to the rearward velocity of the gases produces forward thrust capable of achieving supersonic and even hypersonic flight speeds.
One of the most critical problems encountered at supersonic speeds above Mach 4 is effective mixing of fuel and air in the combustor. If fuel and air do not mix together in overall intimate contact, combustion proceeds at a slower pace. Consequently, full thrust potential is not achieved. To enhance mixing efficiency, turbulence-producing struts have been positioned in the combustor to project into the airstream. However, the losses associated with any such obstructions in the airstream become intolerable at high Mach numbers.
Traditionally, fuel is injected as essentially continuous streams or sprays from a plurality of injectors variously positioned in the combustor of a scramjet engine. That is, fuel flow rate remains invariant over time for a given flight velocity. The inventors herein have determined that, because of the extremely high velocity and pressure of the airstream entering the combustor at high Mach numbers, continuous or steady state injection of fuel achieves only minimal penetration into the airstream and rather poor mixing of fuel and air. Consequently, top speed becomes unduly limited.